Relvar
Encyclopedia
In relational database
s, a relvar is a term coined by C. J. Date as an abbreviation
for the concept of relation variable
, which is the actual term used by the inventor of the relational model
, E. F. Codd, regarding the same concept. The term is used in Date's well-known database textbook An Introduction to Database Systems to differentiate between a variable
that contains a relation and the relation itself.
Relvar is not universally accepted as a term, and it certainly has no meaning in the context of existing database management system
products that support SQL
. Other database textbooks use the term relation (or table) for both the variable and the data it contains. This is most likely because in SQL there are no variables, nor are there assignment operators.
Relational database
A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...
s, a relvar is a term coined by C. J. Date as an abbreviation
Abbreviation
An abbreviation is a shortened form of a word or phrase. Usually, but not always, it consists of a letter or group of letters taken from the word or phrase...
for the concept of relation variable
Relation (database)
In relational model:A relation value, which is assigned to a certain relation variable, is time-varying. By using a Data Definition Language , it is able to define relation variables.The following is an example of a heading which consists of three attributes....
, which is the actual term used by the inventor of the relational model
Relational model
The relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by Edgar F...
, E. F. Codd, regarding the same concept. The term is used in Date's well-known database textbook An Introduction to Database Systems to differentiate between a variable
Variable (programming)
In computer programming, a variable is a symbolic name given to some known or unknown quantity or information, for the purpose of allowing the name to be used independently of the information it represents...
that contains a relation and the relation itself.
Relvar is not universally accepted as a term, and it certainly has no meaning in the context of existing database management system
Database management system
A database management system is a software package with computer programs that control the creation, maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated...
products that support SQL
SQL
SQL is a programming language designed for managing data in relational database management systems ....
. Other database textbooks use the term relation (or table) for both the variable and the data it contains. This is most likely because in SQL there are no variables, nor are there assignment operators.